Air Monitoring

Continuous measurement of mercury emissions in combustion plants (Overview and new measuring method)

Dec 12 2014 Read 785 Times

Free to read

This article has been unlocked and is ready to read.

Download

Introduction

Continuous measuring devices have been used for continuous recording of Hg emissions in waste incineration plants since the early Nineties. Operators of combustion plants must maintain a 24-hour measured value of 30 μg/m³ mercury and a half-hourly average value of 50 μg/m³ in accordance with the 13th and 17th BImschV. In order to meet these requirements, measuring devices used for the measuring ranges 0 – 45 μg/m³ and 0 – 75 μg/m³ must be suitability tested and certified. Apart from waste incineration plants, more and more cement plants and power plants that use substitute fuels for example, fall within the scope of this Directive.

Sample gas conditioning, reduction and existing measurement technology

Existing measurement technology is based on extractive gas sampling, conversion, possibly amalgamation and UV measurement (Fig. 1). Sample gas conditioning plays a special role for mercury measurement. The reason for this is that UV analyzers with atomic absorption spectroscopy usually used can only detect metallic mercury. The flue gas does however not only contain metallic mercury but also oxidized mercury compounds, mainly mercury chloride (HgCl, HgCl2). These compounds cannot be detected directly and must be reduced to metallic mercury through appropriate measures in sample gas conditioning. The total mercury in the flue gas can first be recorded after this reduction. 

Various methods are used for mercury chloride reduction (Fig. 2). One method uses the classic wet chemical reduction, for example, with a tin chloride solution, as also used in laboratories for reference measurements. Another method being used more and more over the past years is the so-called dry reduction. Dry reduction uses converters in gas sampling which convert the oxidized mercury compounds to metallic mercury either at low temperatures (approximately 250° C) or high temperatures (approximately 700° C). The methods used each have advantages and disadvantages, and are rated by operators very differently regarding operating, efficiency and reliability.


Digital Edition

International Environmental Technology January / February 2018

February 2018

In This Edition... Business News - The Swiss Technology Award for the Promass Q Flowmeter is Won by Endress + Hauser - Environnement S.A unveils its new Brand envea - Kipp & Zonen B.V. Sold...

View all digital editions

Events

PITTCON 2018

Feb 26 2018 Orlando, Fl, USA

EKOTECH

Feb 28 2018 Targi Kielce, Poland

IWE Istanbul Water Expo

Mar 01 2018 Yesilkoy-Istanbul, Turkey

SIAF GUANGZHOU

Mar 04 2018 Guanghzou, China

Saudi Downstream

Mar 06 2018 Yanbu, Saudi Arabia

View all events